A telephone handset and base, as well as the base and a wall terminal, are typically interconnected by a telephone cord which is terminated at each end by a modular plug. The modular plugs are inserted into jacks in the base, the handset, and in the wall terminal. Modular plugs are known in the art and are covered by patents such as E. C. Hardesty et al U.S. Pat. No. 3,699,498 which issued Oct. 17, 1972. Telephone cords that are mass produced in a factory environment and terminated with modular plugs, which include a plurality of spaced, parallel terminals in the shape of blades, must be checked for electrical continuity and must be tested for breakdown when they are subjected to a relatively high test voltage of about 1000 volts.
It has been customary to use an apparatus which tests the cord for electrical continuity from one end to the other and then tests for high voltage breakdown. This is generally accomplished with a test set which includes a plurality of relays with contacts being shifted by precise sequential timing devices for testing each successive conductor and for switching from a continuity test mode to a voltage breakdown test mode. In one commonly used apparatus for testing telephone cords, each conductor in sequence is tested for voltage breakdown by impressing a test potential between one conductor and the other conductors which are grounded.
It is difficult to achieve consistently reliable tests over a substantially long period of time with test sets including switching circuits that require precise sequential timing and including relays which have a high frequency of maintenance, especially when used in relatively high voltage circuits. Moreover, when such a test set is controlled to disconnect the continuity test mode and to reconnect to a voltage test mode, there is no guarantee that the cord conductors will be connected to the test voltage because of the possibility of the relay contacts sticking together, which could cause an erroneous indication of the quality of the cord.
The commonly used high voltage breakdown test apparatus includes a plurality of test probes which are adapted to engage the terminals and which are spaced apart in a linear array on centers aligned with the array of spaced, parallel terminals. Quite often in this arrangement, because the terminals may be spaced as close as about 0.10 cm on centers, an arcing occurs between adjacent ones of the test connections which gives a fallacious reading in the test set insofar as voltage breakdown testing is concerned. It would be most desirable to provide a test set for use in a manufacturing environment in which the voltage breakdown testing of plug-terminated cords could be made with confidence in the results and with the same test set which tests for continuity.
Unfortunately, apparently no test apparatus which overcomes the foregoing problems exists in the prior art. The known prior art does include U.S. Pat. No. 3,354,389 which shows an apparatus for testing a plurality of conductors for continuity and shorts, and for voltage breakdown between each successive conductor and the remaining conductors which are grounded by causing appropriate relays to be operated. Another patent, U.S. Pat. No. 3,600,673, relates to a sequentially stepped, multiconductor testing apparatus having switches for connecting high and low voltage currents to circuits under test.
Seemingly, the prior art is devoid of apparatus that provides a solution to the problem of the reliable testing of cords, which are terminated with modular plugs, for continuity and test voltage breakdown, and that advantageously includes elements having a low frequency of maintenance.